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x86/ldt: Fix off by one in get_segment_base()

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ldt->entries[] is allocated in alloc_ldt_struct().  It has
ldt->nr_entries elements and ldt->nr_entries is capped at LDT_ENTRIES.
So if "idx" is == ldt->nr_entries then we're reading beyond the end of
the buffer.  It seems duplicative to have two limit checks when one
would work just as well so I removed the check against LDT_ENTRIES.

The gdt_page.gdt[] array has GDT_ENTRIES entries.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Andy Lutomirski <luto@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: kernel-janitors@vger.kernel.org
Fixes: d07bdfd322d3 ("perf/x86: Fix USER/KERNEL tagging of samples properly")
Link: http://lkml.kernel.org/r/20170818102516.gqwm4xdvvuvjw5ho@mwanda
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Dan Carpenter 2017-08-18 13:30:30 +03:00 committed by Ingo Molnar
parent 9c3a815f47
commit eaa2f87c6b
1 changed files with 2 additions and 5 deletions
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7
arch/x86/events/core.c
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@ -2335,12 +2335,9 @@ static unsigned long get_segment_base(unsigned int segment)
#ifdef CONFIG_MODIFY_LDT_SYSCALL
struct ldt_struct *ldt;
if (idx > LDT_ENTRIES)
return 0;
/* IRQs are off, so this synchronizes with smp_store_release */
ldt = lockless_dereference(current->active_mm->context.ldt);
if (!ldt || idx > ldt->nr_entries)
if (!ldt || idx >= ldt->nr_entries)
return 0;
desc = &ldt->entries[idx];
@ -2348,7 +2345,7 @@ static unsigned long get_segment_base(unsigned int segment)
return 0;
#endif
} else {
if (idx > GDT_ENTRIES)
if (idx >= GDT_ENTRIES)
return 0;
desc = raw_cpu_ptr(gdt_page.gdt) + idx;